Semiconductor devices such as High Electron Mobility Transistors (HEMTs), Schottky diodes, Metal Semiconductor Field Effect Transistors (MESFETS) and the like employ a Schottky contact. Schottky contacts are generally metal contacts that are formed on a semiconductor material to create a metal-semiconductor junction that tends to provide a rectifying effect due to an inherent potential barrier that is formed at the metal-semiconductor junction.
A Schottky contact may be created by forming one or more metal layers on a surface of a semiconductor body where the Schottky contact is desired. For example, a Schottky gate contact for a HEMT may be formed on the semiconductor body and between corresponding source and drain contacts. If the semiconductor material on which the HEMT's Schottky gate contact is formed includes Aluminum Gallium Nitride (AlGaN), two common metals that are often used in the Schottky gate contact of the HEMT are Nickel (Ni) and Gold (Au). More specifically, a Ni layer is typically formed on the semiconductor body of the HEMT, and an Au layer is formed on the Ni layer. Other layers may be provided between the Ni and Au layers. The Ni layer forms a Schottky layer of the Schottky gate contact. Notably, Ni is often used for the Schottky layer of a Schottky contact to an AlGaN material due to the relatively high barrier height provided between Ni and AlGaN. The upper Au layer is formed at or near the top of the Schottky gate contact to form a contact layer. Use of Au for the contact layer helps to minimize resistance associated with the Schottky gate contact.